Estrogens stimulate the synthesis and secretion of the egg yolk precursor protein, vitellogenin, by the avian liver. The proposed study concerns two aspects of vitellogenin synthesis in the avian liver. The first is a study of vitellogenin mRNA levels in the liver during estrogenic stimulation. Complementary DNA to vitellogenin mRNA will be used to examine the accumulation of vitellogenin mRNA during primary and secondary hormone stimulation. The aim of these studies is to (1) Define the lag period between hormone administration and the initiation of mRNA accumulation (2) Examine the kinetics of vitellogenin mRNA accumulation, and (3) Examine the stability of vitellogenin mRNA when hormone stimulation is terminated. The second aspect of the proposed research concerns the synthesis and secretion of vitellogenin by isolated liver cells. Cell suspensions prepared from estrogen stimulated liver will be employed to examine the pathways of synthesis, phosphorylation, and secretion of vitellogenin. Immunohistochemical techniques will be employed to examine the distribution of responsive cells during estrogen stimulation.